The present invention relates generally to adaptive incremental redundant (IR) hybrid automatic repeat request (ARQ) schemes and more particularly to improving throughput in wireless transmission systems using adaptive IR hybrid ARQ schemes.
In most wireless communication systems, the channels are time-varying. In order to maintain high throughput and reliability simultaneously over such time-varying channels, the forward error correction (FEC) codes can be employed with the use of automatic repeat-request (ARQ) schemes, such as a hybrid ARQ scheme. With hybrid ARQ, the receiver first uses FEC codes to correct the errors and triggers the retransmission when residual error is detected. A simple hybrid ARQ scheme is type-I hybrid ARQ, in which the receiver discards the previous transmission and performs the detection and decoding over the retransmitted signal only. Although this scheme saves the buffer size by discarding the previously received packet, it is not an efficient method in term of throughput.
Generally, two types of hybrid ARQ schemes are of particular interest in data packet systems—Chase combining and incremental redundancy (IR) hybrid ARQ (e.g., type-II hybrid ARQ). In the Chase combining scheme, the repeated coded sequence is sent to receiver upon the ARQ request. The receiver then combines received multiple copies of coded sequence using maximum ratio combining (MRC) for the detection. In type-II hybrid ARQ, additional parity bits are transmitted at each retransmission. The receiver performs the decoding using all received sequences since they belong to one codeword. With IR hybrid ARQ, the throughput performance is improved with a coding gain in additional to the diversity gain. Both Chase combining and IR hybrid ARQ schemes provide throughput gain over type-I hybrid ARQ with the expense of additional buffers and complexity at the receiver.
To achieve high throughput efficiency, both Chase combining and IR hybrid ARQ schemes have been adopted in practical wireless systems. They have also been included in recently established wireless standards. Hybrid ARQ can be classified as synchronous and asynchronous. In synchronous hybrid ARQ, the retransmissions are restricted to occur at known time instants. In asynchronous hybrid ARQ, the retransmissions may occur at any time. For asynchronous hybrid ARQ, additional signaling of ARQ process number is required.
In terms of transmission attributes, the hybrid ARQ can be further classified as adaptive and non-adaptive. In adaptive hybrid ARQ, the transmitter may change the attributes at each retransmission including the modulation, coding rate, resource block allocation, etc. In non-adaptive hybrid ARQ, the modulation, coding rate, and the allocated resource block for retransmissions is the same as the original transmission.
Present, existing solutions have considered non-adaptive hybrid ARQ. That is, the block length and modulation in each retransmission is assumed to be the same as that in the original transmission. For adaptive hybrid ARQ, the conventional solutions only consider the binary coded system without employing the discrete quadrature amplitude modulation (QAM).
Accordingly, improved systems and methods for improving throughput in adaptive IR hybrid ARQ wireless transmission systems are required.